Formation of Hydrido–η³‐Allyl Complexes of Ir^III by Sequential Olefinic CH Bond Activation and CC Coupling of Alkenyl and Olefin Ligands

Abstract

Abstract:The bis(ethene) complex [Tp*Ir-(C2H4)J (1*) (Tp* = tris(3,Sdimethyl-1 -pyrazol-1

Investigations on the Coupling of Ethylene and Alkynes in [IrTp] Compounds: Water as an Effective Trapping Agent

“…of DMAD to a solution of the bis(ethylene) complex Tp Me2 Ir(C 2 H 4 ) 2 (1) [9] in CH 2 Cl 2 , at room temperature, produces immediate consumption of 1 and formation of a new compound, 2, as deduced from the NMR spectra of the reaction mixture [Eq. (1)].…”

“…Different pathways could in principle be envisaged for this transformation; nevertheless, we propose that it takes place by direct migration of the hydride to the alkenyl carbon, with concerted or stepwise bond rearrangement along the chain. Compound 3 exhibits 1 H NMR resonances due to the -coordinated allyl moiety [9] at 7.07 (CH), 4.09 and 2.94 (CH 2 ) ppm, the corresponding C atoms producing signals in the 13 C NMR spectrum at 91.2 ( 1 J CH = 170 Hz) and 25.2 ppm ( 1 J CH = 155 and 166 Hz) while the remaining allylic carbon appears at 53.0 ppm. The Ir-bonded alkyl carbon, Ir-C(H)(CO 2 Me)R resonates at 12.0 ppm ( 1 J CH = 135 Hz).…”

“…The 11 B{ 1 H} NMR spectrum shows a singlet at 32.5 ppm, and this value [11] compares well with the corresponding chemical shift recorded for complex 1 (32.9 ppm), which has been shown previously to be a 18-e -species with the Tp Me2 ligand κ 3 coordinated both in the solid state and in solution. [9] Compound 4 is generated by substitution of one of the ethylene ligands in 1 by a molecule of DMAD, a process that also occurs when this derivative reacts with one equivalent of soft Lewis bases (CO and PR 3 ; R 3 = Me 3 , Me 2 Ph, Et 3 ). [12] These reactions have been proposed to occur by an associative mechanism, by means of a change on the coordination mode of the Tp Me2 ligand, from κ 3 to κ 2 .…”

“…As already reported, this compound is fluxional, and this signal represents the average of the chemical shifts corresponding to the axial and equatorial positions, and thus, the 13 C{ 1 H} NMR spectrum recorded for 1 in the solid state exhibits two signals for the ethylene ligands, at 48 and 5 ppm (axial and equatorial, respectively). [9] Probably, the preference of the DMAD for the equatorial position in 4 is because it is a better -acceptor than the ethylene ligand. Although it can not be deduced from the data available, it is proposed that the DMAD ligand does not rotate around the Ir-DMAD axis, due to its strong π-acceptor character.…”

“…of DMAD and 1 equiv. of methyl propiolate, HCCCO 2 Me (MP), in the presence of water, with regioselective formation of the unsymmetrical iridacyclopentadiene Tp Me2 Ir(C(R)=C(R)C(H)=C(R))(H 2 O) (9). Complex 9 reacts with ethylene giving a hydride-alkenyl complex 10, related to 2, in which the C 2 H 4 has inserted regiospecifically into the Ir-C(R) bond that bears the CH functionality.…”